Named for the Archangel Michael, the island was once known as Mont-Tomb. Legend holds that Michael appeared to Aubert, Bishop of Avranches and directed that a church be built on this island. From 966 AD onwards, various French dukes and kings supported the development of a Benedictine abbey on this sacred spot. Over time, cloistral buildings and other structures were added along the steep, cobbled main street, These are now hotels, cafes and shops for visitors.
The abbey is the lovely jewel in this crown and one of the most important sites in Medieval Christian civilization. The Romanesque nave predates most of the rest of the structure, largely built over the Medieval era. Some of the other highlights of the island are the ramparts with their panoramic views; La Chapelle-Saint-Aubert, a small contemplative chapel; the Eglise Paroissiale, and Sant-Pierre, a small chapel midway up the main street to the abbey. The nearly 50 residents still living on Mont St. Michel include monks and nuns of the abbey.
The island experiences powerful tidal variations, when water moves at an astounding rate. During “spring tides” (which can occur any time of year and not necessarily during Spring), access to the island can be stopped for more than an hour. Visitors on the island will not be able to leave until access is restored. So, a bit of research may be necessary before finalizing your schedule. A good tour guide will save you time and make the most of your experience here. I usually use getyourguide.com or viator.com. A visit during a spring tide can be quite exciting, and whether on the island or on shore, the sight is staggering. You can park in the Mont-Saint- Michel lot for a nominal fee and get free shuttle service to and from the site.
I would also recommend staying nearby. The villages of Saint Malo, a lovely seafront village, or Rennes known for its half-timbered Medieval houses and the Rennes Cathedral are a good base to explore this unique region. This whole area is full of beautiful historic villages. Mont-Saint-Michel can be done as a daytrip out of Paris, but staying in French countryside has an incomparable charm.